Question: 5 pencils cost $8.40. Which equation would help determine the cost of 7 pencils?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. If we let $x$ represent the cost of 7 pencils, we have the following proportion: $\dfrac{x}{7}$ We have to pay $8.40 for 5 pencils, and that can be written as a proportion: $\dfrac{\$8.40}{5}$ Since the price per pencil stays the same, these two proportions are equivalent. $\dfrac{x}{7} = \dfrac{\$8.40}{5}$